1. Field of the Invention
The present invention relates to spray-discharge pumps such as the pumps of the so-called aerosol type which are employed for extracting a predetermined quantity of a liquid from a storage container and discharging it to the exterior through a spray-discharge head which is usually equipped with a vertical flow nozzle. Among the pumps of the type considered, the invention is more particularly concerned with those in which the dose of liquid withdrawn is subjected to preliminary compression before being discharged to the exterior.
2. Description of the Prior Art
Pumps of this type have a compression chamber formed within a pump body between a valve having the function of closing the orifice through which liquid is withdrawn from the storage container and an orifice through which the withdrawn liquid is expelled to the spray-discharge head. The compression chamber has a variable volume since it is limited by a piston carried by an element which is capable of axial displacement within the pump body. This element is connected to the spray-discharge head in such a way that a pressure exerted manually on the head by the user in opposition to resilient restoring means makes it possible to initiate operation of the pump.
The invention meets the need to improve the operation of pumps of this type, especially in order to ensure free spray discharge of the liquid in a predetermined dose, in order to avoid dripping or running at the end of a spraying operation or outside periods of use, and in order to permit simple and rugged construction while guaranteeing efficient operation over a long period of service.
These objectives are achieved by the invention, essentially by resorting to an arrangement which produces a precompression effect and involves the use of two chambers, one of which is a variable-volume compression chamber which is internal to the moving element whilst the other chamber is external to said moving element and establishes a communication with the discharge orifice located at the end of the moving element by means of longitudinal ducts formed annularly in said element. Moreover, a needle-valve piston is mounted within the moving element but outside the inner chamber so as to close the discharge orifice when the pressure of liquid within the outer chamber provided with the communication ducts has fallen to zero. This needle-valve piston or precompression piston also performs the function of a snifting piston which prevents running at the start of a spraying operation by virtue of the fact that it is urged by associated resilient means to a position of closure of the discharge orifice, the piston being freed from the orifice when the liquid is put under pressure within the outer chamber or intermediate chamber.
The invention advantageously involves a secondary feature of the pump which is accordingly capable of changing from a single-acting to a double-acting mode of operation. In accordance with this secondary feature, a free-running piston provided within the inner chamber of the main piston or driving piston is thrust by resilient means into a position in which it cuts-off the communication between the inner chamber and the outer chamber and is subsequently moved away from this position only under the action of a pressure of liquid within the inner chamber. When a pump of this type is in operation, a first part of the dose of liquid withdrawn is discharged through the outer chamber when the piston is caused to move downwards in the direction of compression within the inner chamber whilst the remainder of this dose is discharged during upward return of the driving piston which is subjected to the associated resilient means.
In the practical construction of the pump, the different resilient means are usually helical metal springs. However, the free-running piston of the double-acting pump is preferably urged to its closed position by tongues of elastic material molded with a transverse partition-wall which is formed internally of the moving element and limits the inner chamber. In addition, the spring associated with the needle-valve piston is applied against the opposite face of the partition-wall.
So-called "double-acting" precompression pumps are known in which a first part of the withdrawn dose of liquid is discharged through an outer chamber when the piston is caused to move downwards in the direction of compression within an inner chamber whilst the remainder of the dose considered is discharged at the time of upward return of the driving piston which is subjected to the associated resilient means.
A pump of this type is known and has been disclosed in particular in European patent Application No. 0127449 in which leak-tightness between the outer chamber and the inner chamber is ensured by means of an elastic sleeve which is intended to close the communication orifices between the two chambers. In the solution proposed in the cited patent Application, the sleeve is provided with grooves which put an intermediate chamber into communication with the liquid discharge duct. Moreover, the moving element which actuates the driving piston whose intended function is to vary the internal volume of a first compression chamber acts on the driving piston by means of this sealing element. There therefore exists an incompatibility between the elasticity which the sleeve must have in order to ensure leak-tight flow of the fluid from the first compression chamber to the intermediate chamber and the concomitant need to ensure that the sleeve has sufficient rigidity to be capable of transmitting the mechanical effort required for downward displacement of the piston in order to reduce the internal volume of the first chamber and to vary the volume of the intermediate chamber.
A further object of the invention is to propose a precompression pump which makes it possible to ensure a high standard of leak-tightness between a first inner chamber and a second chamber while having elements of simple constructional design which can readily be mounted.